Embodiments of the present specification relate to semiconductor power switches, and more particularly to a gate driver circuit for controlling switching of the semiconductor power switches.
Power switches such as insulated gate bipolar transistors (IGBTs), reverse conducting IGBTs, bi-mode insulated gate transistors (BiGTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), and the like, have been used in applications that entail use of high power, high voltage, or high current. Some examples of such applications include, but are not limited to, power converters such as inverters, rectifiers, choppers, and Direct Current (DC)-DC converters. In these applications, switching timing of the power switches employed therein play an important role in the performance of the power converters.
A power switch module such as an IGBT module typically includes a freewheeling diode coupled in antiparallel with an insulated gate bipolar transistor (IGBT). Moreover, transitioning the IGBT to an ON-state includes three phases, such as a delay phase, a commutation phase, and a saturation phase. Therefore, a “switch-on” time of the IGBT is a sum of durations of the delay phase, the commutation phase, and the saturation phase.
As will be appreciated, a gate driver circuit aids in controlling the switching of the power switches used in the power switch modules which may in turn be employed in an inverter circuit, for example. The power switches used in the inverter circuit may include IGBTs. A gate driver circuit is typically employed to control gate voltages of the IGBTs for controlling the switching of the IGBTs in the inverter circuit.
In operation, the gate driver circuit supplies a gate voltage to a gate terminal of the IGBT through a resistor (hereinafter referred to as a gate resistor). Typically, the value of the gate resistor is a fixed value. For example, the gate resistor may be selected such that the IGBT performs satisfactorily in a worst case condition. More particularly, the value of the gate resistor is typically selected such that the freewheeling diode in the IGBT module is protected from stresses induced in the commutation phase. Such a value of the gate resistor thus aids in maintaining a lower slew rate of a current flowing through the freewheeling diode and thereby protects the freewheeling diode. However, use of such fixed configured gate resistors also leads to decreased performance of the IGBT in the delay phase and the saturation phase due to long delay times and high switching losses. Moreover, such decreased performance of the IGBT in the delay phase and saturation phase hampers operability of the gate driver circuit in applications where high speed switching is required. As faster switching time is a factor in many applications aimed at higher efficiency, the industry requires gate drivers that do not suffer from the noted deficiencies.